Method for producing catalysts by acid activation

ABSTRACT

A process for producing catalysts by acid activation of phyllosilicates and coating with catalytically active metal ions wherein the acid activation is carried out in the presence of catalytically active metal ions. The solution which forms during acid activation together with the remaining solution which contains the excess, catalytically active cations are separated. The catalysts can be used for proton-catalyzed and Lewis acid-catalyzed reactions, especially for conversion of higher olefins with aromatic hydroxy compounds and amines, for esterification and dehydration reactions and for purification of aromatics.

The invention relates to a process for producing catalysts by acidactivation of phyllosilicates and modification with catalytically activemetal ions.

Catalysts based on phyllosilicates, for example, clays, are used in manytechnical reactions. But naturally occurring clays, such as for examplemontmorillonite, kaolin, or attapulgite, in part have overly lowactivities. For this reason the clays for producing catalysts are oftenactivated by treatment with acid. On the one hand, pure covering withfor example sulfuric acid and, on the other hand, activation byextraction of the raw clay with acid, generally sulfuric or hydrochloricacid, can be done.

Thus, according to U.S. Pat. No. 3,452,056 an acid-coveredmontmorillonite catalyst (KSF/0) is used for alkylation ofdiphenylamine. According U.S. Pat. No. 5,672,752 an acid-extractedmontmorillonite is used for the same reaction. Catalysts of this typeare available under the commercial name Retrol, Fulcat and K10.According to U.S. Pat. No. 5,043,511, as a replacement for corrosivehomogeneous catalysts, for example AlCl₃ or BCl₃, heterogeneouscatalysts are used which are produced by coextrusion of clays with twodifferent metal salts and thermal treatment at temperatures from 300° C.to 800° C. Products produced in this way are used as catalysts foralkylation of, for example, benzene with olefins.

But these modified clays also have disadvantages, for example, rapiddeactivation or a complex production process, and there have been manyefforts to eliminate these defects. Thus, U.S. Pat. No. 2,464,127reports on a two-stage process with the object of obtaining amounts ofiron as small as possible in the end product of acid activation ofmontmorillonite. According U.S. Pat. No. 2,574,895, some of the saltsextracted in acid treatment are precipitated again on themontmorillonite-containing material, reducing reagents which areintended to prevent the iron from settling in the precipitation processbeing used. The effort to increase the service life of the resultingcatalysts by reduced coke formation is common to both applications.

DE-A-1 271 682 describes a process for activation of montmorillonites byacid extraction in the presence of inert organic liquid compounds.Strong acids, such as for example hydrochloric or sulfuric acid, areused for acid activation. Due to the presence of organic componentsduring decomposition of the clay by acid, the lattice distances of theresulting montmorillonite catalyst are increased, by which more catalystcenters become accessible to the substrate. The catalysts according toDE-A-1 271 682 are used for alkylation of phenolic compounds.

Other methods of activation are described in EP-A-352 878. In this casean untreated clay is covered by impregnation with, for example, zincsalts, copper salts or nickel salts. Organic solvents of the metal saltsare used. The solvent is removed by distillation after impregnation.According to EP-A-144 219 and EP-A-031 252 raw clays are activated by asimilar impregnation technique or by ion exchange. In ion exchange thenatural intercalate cations of the minerals, mainly sodium, calcium andmagnesium, are replaced by catalytically active metals. The disadvantagein this process is that the catalysts produced have an overly low porevolume. This means that only the outer surface is accessible to thesubstrates. Most of the inner surfaces of the catalysts are, however,not accessible. Thus, a large part of the possible activity remainsunused.

To overcome this disadvantage, Laszlo in Helvetica Chimica Acta 70(1987) 577 describes subsequent metal ion activation of alreadyacid-activated montmorillonites. Thus, the commercially availablecatalyst K10 which is rich in pores and which is produced by acidactivation of bentonite is modified by ion exchange with various metalsalts. To do this the K10 present as a powder in a methanolic slurry istreated with solutions of the metal salts for several hours. The amountof metal ions used is computed such that they are present in a roughly30- to 40-fold excess relative to the ion exchange capacity of the K10.Then the mixture is separated by filtration and the catalyst is washedfree of salts and then dried. Especially good effects are achieved byion exchange with aluminum salts and titanium salts. Replacement withiron salts leads to improved reactivity of the catalyst only in a fewcases.

A similar process is also used by Cativiela in Appl. Cat. A 123 (1995)273. Cativiela calcinates the catalysts additionally at temperaturesaround 500° C. in order to reduce the Bronsted activity. In thispublication good activities are achieved especially with cerium salts.Replacement with iron ions however does not show any special effects.

The process used in these activation methods has at least twodisadvantages. On the one hand, the process consists of two componentprocesses which are independent of one another, specifically the acidactivation of raw clays and the subsequent ion exchange reaction.Secondly, the ion exchange reaction must be carried out at a high ionexcess. This necessarily leads to highly burdened waste water flows. Inaddition, the amounts of wash water necessary to clean the initialproduct after acid activation and for washing after ion exchange arevery large, so that large amounts of waste water are formed thereby.

EP-B 284 397 describes a process in which the clay to be activated bythe ion exchange is replaced in an upstream step with lithium ions andthen thermally treated. With the resulting intermediate product ionexchange is then carried out in a second process step. Metal ions whichare preferably used for this purpose are aluminum ions. Li clays withreplaced iron ions do not show any improved activity compared to theinitial material.

The object of this invention was to produce catalysts which have beenmodified with metal ions, and simple process steps and small waste waterflows were to be guaranteed.

The subject matter of the invention is thus a process for producingcatalysts by acid activation of phyllosilicates and modification withcatalytically active metal ions characterized in that the acidactivation is carried out in the presence of catalytically active metalions. The solution which is formed during acid activation together withthe residual solution which contains the excess, catalytically activecations are then separated.

It has been surprisingly found that highly active catalysts can beobtained from the acid activation of phyllosilicates in the presence ofactivating ions. In doing so it is not necessary to carry out activationand ion exchange in separate process steps. In the process as claimed inthe invention, unexpectedly small amounts of the catalytically activeions are necessary. This process reduces process costs, and reduces theenvironmental burden of the process to a minimum. In certain cases, asfor example with activation with iron ions or aluminum ions, the spentliquors obtained can even be used as precipitation aids in the clean-upof municipal sewage. It has furthermore been ascertained that the metalions used for modification are present in an especially high degree ofactivation so that the amount of metal ions present in the final productcan be kept especially low.

The subject matter of the invention is also the use of catalystsobtained using the process as claimed in the invention forproton-catalyzed reactions, especially for conversion of higher olefinswith aromatic hydroxy compounds and amines, for esterification anddehydration reactions as well as for purification of xylene and forLewis acid-catalyzed reactions, such as for example alkylation ofaromatics.

The invention is illustrated by the following examples.

EXAMPLE 1 Comparison Catalyst

A previously dried Bavarian montmorillonite-containing raw clay with anion exchange capacity (IEC) of 80 mVal/100 g was decomposed byhydrochloric acid treatment.

To determine the ion exchange capacity (IEC), the phyllosilicate to bestudied was dried over an time interval of 2 hours at 150° C. Then thedried material was reacted with an excess of aqueous 2N NH₄Cl solutionfor one hour with reflux. After a holding time of 16 hours at roomtemperature it was filtered, whereupon the filter cake was washed, driedand ground and the NH₄ content in the phyllosilicate was determined bynitrogen determination (CHN analyzer from Leco). The proportion and typeof exchanged metal ions was determined in the filtrate by ICPspectroscopy.

During decomposition, 90.3 g of raw clay with a water content of 16.9%by weight together with 250.7 g water and 87.5 mg of 30% hydrochloricacid were treated in a three-neck flask with a reflux condenser for 8hours at boiling. Afterwards the mother liquor was separated from theproduct by filtration by means of a Buchner funnel and washed usingdemineralized water until chloride could no longer be detected in thewash water. The washed filter cake was dried at a temperature of 120° C.and then ground.

The product obtained in this way has a BET surface area of 253 m²/g(according to DIN 66131) and a pore volume of 0.403 ml/g (determined bynitrogen adsorption and evaluation of the adsorption isotherms using theBJH method—E. P. Barret et al., J.Am.Chem.Soc. 73 (1951) 373). The poredistribution curve obtained from BJH derivation showed a Gaussiandistribution with a maximum at 5.5 nm. The material contained amongothers the following exchangeable metal ions:

Fe³⁺ 1.0 mVal/100 g Al³⁺ 11.4 mVal/100 g Ce³⁺ <0.1 mVal/100 g

EXAMPLE 2 Iron-Containing Catalyst

A Bavarian montmorillonite-containing raw clay with an ion exchangecapacity IEC of 92 mVal/100 g was activated analogously to Example 1. Inaddition to the reagents indicated in Example 1, iron chloride in theform of a concentrated FeCl₃ solution was added to the batch. Thefollowing were used for this batch:

Raw clay (17.2% by weight H₂O) 82.8 g Water 250.3 g HCl (30%) 50.0 gFeCl₃ solution (2.5 mole Fe/kg) 6.0 g

The product obtained in this way had a BET surface area of 290 m²/g anda pore volume of 0.338 ml/g. The peak of the pore distribution curve wasat 4.6 nm. The amount of exchangeable Fe³⁺ ions was 2.0 mVal/100 g.

EXAMPLE 3 Iron-Containing Catalyst

Example 2 was repeated using 18.0 g FeCl₃ solution:

The product obtained in this way had a BET surface area of 400 m²/g anda BJH pore volume of 0.491 ml/g. The peak of the pore distribution curvewas at 4.7 nm. The amount of exchangeable Fe³⁺ ions was 8.0 mVal/100 g.

EXAMPLE 4 Aluminum-Containing Catalyst

Example 2 was repeated using 7.24 g AlCl₃*6H₂O.

The product obtained in this way had a BET surface area of 315 m²/g anda BJH pore volume of 0.425 ml/g. The peak of the pore distribution curvewas at 3.3 nm. The product contained 18.0 mVal/100 g exchangeable Al³⁺.

EXAMPLE 5 Cerium-Containing Catalyst

A montmorillonite-containing raw clay from Turkey was dried to a watercontent of roughly 15% by weight and was ground. The material with aresulting water content of 13.1% by weight was activated as described inExample 1, the reaction mixture having been enriched with Ce(NO₃)₃*6H₂O.The following were used for this batch:

Raw clay (13.1% by weight H₂O) 86.3 g Water 254.6 g HCl (30% by weight)62.5 g Ce(NO₃)₃.H₂O 13.03 g

Analysis of the product yielded a BET surface area of 379 m²/g and a BJHpore volume of 0.431 ml/g. The peak of the pore distribution curve wasat 3.0 nm. The product contained 5.1 mVal/100 g exchangeable Ce³⁺.

EXAMPLE 6 Reaction of Phenol with Nonene

The alkylation reaction, example 11 from DE-A-1 271 682 was reworkedanalogously. In a 1 liter three-neck flask equipped with a thermometer,a magnetic stirring mechanism and a reflux condenser, 252.5 g (2.0 mole)nonene, 235.3 g (2.5 mole) phenol and 5.0 g catalyst from Example 2 andExample 3 were heated to 90° C. After 3 hours reaction time, thecatalyst was filtered off. The filtrate was fractionated using a 10 cmVigreaux column. In the boiling range from 159° C. to 181° C. thealkylation product nonyl phenol was obtained.

As Table I shows, higher yields were achieved with the catalysts asclaimed in the invention compared to the undoped catalyst (Example 1).The narrower boiling range for Fe-modified catalysts indicates a moreuniform product spectrum and thus higher selectivity of theFe-containing catalysts.

TABLE I Alkylation of Phenol with Nonene Catalyst Boiling range ofproduct Yield Example 1 160–180° C. 35.3% Example 2 165–175° C. 38.7%Example 3 173–175° C. 41.2%

EXAMPLE 7 Reaction of Diphenylamine with Nonene

In a 500 ml three-neck flask, 42.5 g (0.25 mole) diphenylamine wereheated to roughly 150° C. and melted. Then 5.0 g catalyst and 44.2 g(0.35 mole) nonene were added to the melt. After a reaction time of 4 h,a further 41.6 g (0.33 mole) nonene were added, the reaction temperatureof 150° C. having been maintained. After a reaction time of 8 h thereaction mixture was separated from the catalyst by filtration. Theyield of dialkylated diphenylamine was determined by infraredspectroscopy using the following formula:(%) dialkylate=[Log(ext@ 820 cm^(−1/) ext@ 743 cm⁻¹)+1.141]/0.019;ext@ extinction (absorbance) at the indicated wave number. In doing soit was considered that the adsorption peak at 820 cm⁻¹ corresponds tothe dialkylated products, and the adsorption peak at 743 cm⁻¹corresponds to the monoalkylated products. The reaction mixture wasmeasured at a layer thickness of 0.025 mm to determine extinction.

Table II lists the determined yields of the reaction with variouscatalysts.

TABLE II Alkylation of Diphenylamine with Nonene Catalyst Yield ofdinonyl-diphenylamine (%) Example 1 27 Example 3 40 Example 4 37 Example5 35

The example confirms the improved activity of the catalysts as claimedin the invention in diphenylamine alkylation compared to the prior art.

EXAMPLE 8 Esterification of Acetic Acid and Ethanol

In a 250 ml three-neck flask with a thermometer, a magnetic stirringmechanism and a reflux condenser, 72.0 g acetic acid and 55.2 g ethanolwere mixed. Roughly 0.5 g was removed from the mixture, and the acidcontent was determined by titration with 0.1N sodium hydroxide solutionagainst phenolphthalein. The educt mixture was heated by means of an oilbath to 85° C. and after reaching the temperature, it was exposed to1.26 g catalyst (relative to the dry substance). With the addition ofthe catalyst a stopwatch, which was used to determine the reaction time,was started. Every 30 minutes roughly 0.5 to 1 g of sample at a time waswithdrawn using a pipette. The small amounts of catalyst entrained inthe sampling did not significantly influence the progression of thereaction and titrimetric acid measurement. Table III shows the measuredconversions after 30 and 60 minutes reaction time.

TABLE III Esterification of Ethanol and Acetic Acid Conversion afterConversion after 30 min (%) 60 min (%) Example 1 10 13% Example 2 2028    Example 4 27 34   

EXAMPLE 9 Dehydration of Cyclohexanol

In a three-neck flask with an attached Vigreaux column and distillationbridge, 250 ml cyclohexanol together with 5 g powdered catalyst asdescribed in Example 3 and Example 5 were caused to boil. The products,cyclohexene and water, which formed during the reaction werecontinuously removed from the reaction space via the distillationbridge. The condensed amounts of water and cyclohexene were recorded asa function of the reaction time. After roughly 200 ml cyclohexanol werereacted, 250 ml substrate was again added to the reaction vessel. Thisprocess was repeated three times without a significant decrease of thereaction rate being observed. The product formation rate for thecatalyst according to Example 3 was 1.9 ml/min, for the catalystaccording to Example 5 it was 1.7 ml/min.

The example confirms the consistently high reactivity of the catalystsfor proton-catalyzed reactions.

EXAMPLE 10 Continuous Purification of Xylene

Some of the filter cake obtained after washing the product according toExample 5 was dried at 110° C. and carefully crushed. The 0.25 mm to0.50 mm grain fraction was screened out of the fragments. Fivemilliliters of these fractional granulates was placed in a 10 ml tubereactor through which industrial xylene flowed continuously via a HPLCpump. The tube reactor was heated by a temperature-controlled oil bathto 175° C., this temperature being kept constant during the experiment.To prevent gas bubble formation at this temperature, a back pressureregulator which regulated the working pressure in the reactor constantlyto 30 bar was installed between the reactor and the likewise installedsampling valves. A LHSV (liquid hourly space velocity) value of 12 h⁻¹was set via the HPLC pump.

The industrial xylene used has a bromine index of 580 mg/100 g due tothe unsaturated aliphatic compounds. These unsaturated compounds werereacted on the granulated catalyst presumably by a Lewis acid-catalyzedalkylation reaction such that after treatment of the raw material thebromine index dropped to values less than 2 mg/100 g. Over time,deactivation of the catalyst which allowed the bromine index of thetreated xylene to rise again took place. After reaching a bromine indexof 20 mg/100 g, exhaustion of the catalyst was defined. The amount ofxylene converted during this running time is a direct measure of thecatalyst activity. Using the granulated catalyst as shown in Example 5,a running time of 18 days was achieved, a total of 25.86 l xylene havingbeen converted. In a comparison test with a commercially availablecatalyst, the Süd-Chemie product Tonsil® CO 630 G, a total running timeof 12 days with a xylene throughput of 17.24 liters was achieved duringthis time.

The example confirms the clear improvement of catalyst activity comparedto the prior art.

1. A process for producing catalysts comprising preparing a mixture of aphyllosilicate and an activating acid; adding iron cations to themixture of the phyllosilicate and the activating acid; activating thephyllosilicate by use of the activating acid in the presence of the ironcations by boiling the mixture; separating a solution formed during theacid activation which contains excess iron cations from the activatedphyllosilicate to produce the catalysts.
 2. The process of claim 1wherein the phyllosilicates are selected from the group consisting ofsmectites, chlorites, illites, vermiculites of the serpentine-kaolingroup and of the sepiolite-palygorskite group including montmorillonite,beidellite and nontronit.
 3. The process of claim 1 wherein the acidactivation is carried out in the presence of an earlier acid activationsolution, which solution contains aluminum ions.
 4. The process of claim1 wherein the acid activation is carried out in the presence of anearlier acid activation solution, which solution contains aluminum andiron ions.
 5. The process of claim 1 wherein the phyllosilicates afteracid activation in the presence of catalytically active cations arewashed, dried and calcined.
 6. The process of claim 1 wherein the ironions are added to the mixture of phyllosilicate and activating acid inthe form of a solution.